Hot-film air-mass meters can be used to detect the air mass drawn in by internal-combustion engines. These meters have a heated element, which is situated in the air flow to be measured and is cooled in this manner. In particular, it is possible to use the heated element as part of an electric bridge circuit and to keep it at a constant overtemperature relative to the intake air temperature by means of a current flowing through this element. With this principle, the required heating current is a measure for the air mass drawn in by the engine. The pulsations of the intake air, which possibly occur in certain operating ranges of an internal-combustion engine, can cause the measuring result to be corrupted. This is particularly the case when a so-called backflow occurs, since the hot-film air-mass meter cannot distinguish the direction of flow.
It is generally known to provide a hot-film air-mass meter with an evaluation circuit, so that a backflow can be recognized using programming technology. A high computing power is required for this. The backflow is recognized from the evaluation of the signal waveshape.
Furthermore, when backflows occur, it is known to adjust the output signal from a hot-film air-mass meter with a correction value. In certain operating ranges, however, only a very inaccurate result is able to be attained.